1. Field of the Invention
The invention relates to an electronic unit comprising a processor, data input-output means, and cryptographic means; it relates more particularly to a new arrangement of these subsystems that speeds up the cryptographic processing of certain data.
2. Description of the Related Art
One prior art electronic unit incorporating cryptographic means is based on a processor associated with different memories (RAM, ROM and EEPROM, for example) and connected to input-output means. The processor is connected to the cryptographic means via a memory register. The cryptographic means generally comprise electronic circuits dedicated to cryptographic calculations and specifically designed to carry out those calculations very quickly. The operations carried out are, for example, encryption and decryption operations using a DES protocol. In the field of microcircuit cards, there exist very light cryptographic units containing of the order of 5 000 logic gates capable of carrying out DES calculations in just 16 clock pulses. By comparison, copying 8 bytes into a register necessitates 48 clock pulses (8 bytes is the length of a word in DES encryption). The input-output means comprise a UART interface, for example, exchanging information with devices external to said electronic unit in accordance with the ISO7816 or Universal Serial Bus (USB) protocol. The UART interface comprises a register. Prior art cryptographic means (usually referred to as a cryptographic calculation unit) are connected directly to the processor, which manages all aspects of the transfer of the data to be encrypted or decrypted to the cryptographic means, the execution of the encrypting/decrypting operations, and the sending of the results back to the input-output means. Clearly this mode of operation, which monopolizes the processor in each step, is relatively slow and involves a relatively high consumption of energy. The invention overcomes these drawbacks.